This invention relates to an exposure reflective mask for use in the manufacture of semiconductor devices or the like and further relates to a reflective mask blank serving as a base for manufacturing such a reflective mask.
In recent years, with the increase in integration of semiconductor devices, fine patterns exceeding the transfer limit of the photolithography have been required in the semiconductor industry. In view of this, the extreme ultraviolet (EUV) lithography being an exposure technique using EUV light with a shorter wavelength is expected to be promising. Herein, the EUV light represents light in a wavelength band of the soft X-ray region or the vacuum ultraviolet region and, specifically, light having a wavelength of about 0.2 to 100 nm. As a mask for use in the EUV lithography, there is proposed an exposure reflective mask described in, for example, JP-A-H08-213303 (Patent Document 1).
The proposed reflective mask has a multilayer reflective film formed on a substrate and adapted to reflect exposure light, a buffer film formed on the multilayer reflective film, and an absorber film formed in a pattern on the buffer film and adapted to absorb the exposure light. The buffer film is provided between the multilayer reflective film and the absorber film for the purpose of protecting the multilayer reflective film in pattern forming and correcting processes of the absorber film. The exposure light incident on the reflective mask placed in an exposure apparatus (pattern transfer apparatus) is absorbed at a portion where the absorber film is present, but is reflected by the multilayer reflective film at a portion where the absorber film is not present so that a reflected optical image is transferred onto a semiconductor substrate through a reflective optical system.